What to do if your furnace stops working

Put on a parka but don’t panic! Here's what to do

It’s 10 o’clock at night and -30 C, not counting the windchill. Do you know what you’d do if your furnace stopped working?

“Freeze” is the wrong answer.

To learn the right answer, and not be left out in the cold, we checked with Nick Weran (Sheet Metal Worker ’01), owner of City Furnace Mechanical, which he started in 2003 and has grown to include three other staff, including gasfitters and plumbers.

As long as the electricity and gas are flowing, he says, there may be more that you can do to restore the heat than you think.

Here are five things to do should that precious appliance fail you.

1. Turn on your thermostat

thermostat malfunctioning“Come on,” I say, when Weran tells me to make sure the furnace is on. What kind of tip is that?

A good one, it turns out.

“I ask people [who call me] on the phone all the time and it’s in the off position. It’s a thing. It really is,” he says. “You want to make sure that it is in the on position, that it’s turned up and calling for heat.”

2. Check whether there’s power

electrical switch for furnace

We all know that most furnaces won’t work without natural gas, but they need electricity, too, which runs parts such as the blower motor that pushes air through the ducts.

In addition to the breaker, “There should be a switch on the wall or ceiling nearby,” says Weran. Make sure that switch is on. Then, if “the blower motor is on, but it’s blowing cold air, you know that it has power.”

Then keep investigating.

3. Unblock the vents

icy furnace ventsModern furnaces have two pipes leading outside. One is exhaust, the other is air intake.

If the former is blocked, bad things like carbon monoxide may not be properly vented.

(Make sure there’s a CO detector on every floor of your home, Weran adds, including in the room that contains your furnace.)

If the intake is blocked, the furnace will simply shut down. Fish around inside both pipes to keep them free of snow, ice or other debris, says Weran.

4. Change your filter

Common, one-inch-thick filters should be changed at least every three months, says Weran (five- and six-inch varieties can last up to six months).

The filter’s job is to clean the air before it enters the furnace. Over time, it fills with dirt and debris. Too much, and it becomes “like cardboard,” says Weran, preventing fresh air from entering.

As a result, the furnace gets too hot, tripping a safety sensor that shuts everything down.

5. Get someone to take a look – but not just anyone

furnace maintenance

“If those four things are good, then you’re probably going to have to call a service tech, because then we’re getting into an internal problem.”

Before you say yes to the tech, however, Weran recommends checking costs. The urgency that comes of having a furnace on the fritz may make you vulnerable to paying more for a fix than necessary. Ask about charges for

  • The service call. How much is it for a tech to drop what they're doing and make an emergency housecall? Expect around $100 for that alone, says Weran.
  • A diagnostic fee. In some cases, a company will offer a ‘free’ service call. Instead, they may charge you for the details about what’s gone wrong. Weran has heard of some of these fees coming in near $200.
  • Hourly rates. This includes labour and travel time to your home, and to the shop and back for parts. Weran says to expect $95 to about $130 per hour.

No matter what, he stresses, every charge on a bill should be clearly accounted for.

Whatever you do, don’t open up your furnace on your own and start nosing around.

“You need training when you’re dealing with a gas appliance,” says Weran. “If you do something wrong, you could cause a real hazard.”

How long should a furnace last?

Modern furnaces should be replaced after about 20 years, says Weran.

“They don’t make them like they used to. Some furnaces from the ’70s run for 50 years because there’s nothing to go wrong – they’re very simple. Now, furnaces are quite a bit more complicated.”

Safety is the reason. New models are equipped with devices that ensure that the flame doesn’t leave the furnace, that there’s a flame at all, that overheating doesn’t happen, and so on. These parts are essential but not infallible.

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